The present invention relates to a positioning-controlling apparatus for positioning a subject by moving it to a predetermined position and a positioning-controlling method, and part-mounting equipment and a part-mounting method which comprise the positioning-controlling apparatus or employ the positioning-controlling method.
In part-mounting equipment for continuously mounting parts such as electronic parts, etc. on determined positions of a circuit-formed material such as an electronic circuit substrate or the like, a part is mounted on a determined position of a circuit-formed material by introducing the circuit-formed material into the equipment and regulating and holding it, while carrying and positioning a part at a determined position of the circuit-formed material, and mounting the part thereon. Alternatively, if a position to receive a part is specified, a circuit-formed material is carried and positioned so as to mount the part on a determined position of the circuit-formed material at the above specified position. FIG. 7 shows an essential portion of part-mounting equipment comprising the former type positioning means which carries a part and positions it.
As seen in FIG. 7, part-mounting equipment (100) essentially consists of a part-supplying unit (50) for supplying parts to the part-mounting equipment (100), a robot (60) for carrying a subject on an X-Y plane, a mounting head (75) to be carried by the robot (60), a circuit-formed material-holding device (80) for carrying and holding a circuit-formed material, and a controller (90) for controlling the overall operation of the part-mounting equipment (100).
The robot (60) comprises a Y-direction driving unit which causes motors (62 and 64) fixed on the equipment to move a beam (70) along ball screws (63 and 64) in the direction Y, and an X-direction driving unit which causes a motor (72) fixed on the beam (70) driven by the Y-direction driving unit to move the mounting head (75) along a ball screw (73) in the direction X. In this regard, although the Y-direction driving unit may comprise a system in which driving is performed using one motor and one ball screw, Y-direction driving units of a multi-screw driving system (in this drawing, a twin-screw type using two ball screws (63 and 65)) have come into wide use to meet the latest demand for high-speed and high-load mounting performance, and also to achieve high rigidity and high accuracy of equipment.
As seen in FIG. 7, the mounting head (75) has 4 mounting nozzles (76) which are movable up and down along the direction Z and rotatable on the axis Z as the center. By this motion of the nozzles (76), parts are taken out and mounted. The circuit-formed material-holding device (80) carries a circuit-formed material such as an electronic circuit substrate (82) as shown in FIG. 7 into the part-mounting equipment and regulates and holds the substrate (82) at a predetermined position in the course of mounting the part.
The part-mounting equipment (100) arranged above is operated as follows. The mounting head (75) with the respective mounting nozzles (76) which suck parts from the part-supplying unit (50) and hold them is carried to a mounting position by the robot (60), while the circuit-formed material-holding device (80) introduces the electronic circuit substrate (82) and holds it at a predetermined position. The distance which the robot (60) travels carrying the mounting head is computed and controlled by the controller (90) based on the data of a condition of the part sucked and held by the mounting nozzle (76), which is separately recognized, and data of a condition of the electronic circuit substrate (82) held. The mounting head (75), which is moved to the mounting position and stopped there, lowers the mounting nozzles (76) so as to mount the parts sucked at the ends of the nozzles (76) on the mounting positions of the electronic circuit substrate (82).
Part-mounting equipment is typically provided with a positioning-controlling apparatus for moving a subject (the mounting head (75) in the case of the X-direction driving unit shown in FIG. 7) in a predetermined direction along the ball screw which is rotated by a servo motor, and positioning it at a predetermined position and stopping it there. The system for detecting the position of the subject in this positioning-controlling apparatus is classified as a rotary encoder system in which the position of a subject is detected based on the number of rotations of a rotary encoder which rotates coaxially with a servo motor shaft, and a linear encoder system in which a position of a linear scale attached parallel to a direction along which a subject is moving is detected by a linear position-detecting device attached on the subject.
Recently, techniques for miniaturizing parts have been advanced, and hence high-density mounting of parts on an electronic circuit substrate has been realized. Therefore, accurate positioning and mounting of parts are required for part-mounting equipment. Under such circumstances, a positioning-controlling apparatus for use in part-mounting equipment tends to employ the linear encoder system capable of more accurately detecting a position of a subject than the rotary encoder system. The linear encoder is further classified as one of two types: one is an absolute type encoder which detects an absolute position by counting, and the other is an incremental type encoder which detects a relative position by counting. Of these encoders, presently, the incremental type encoder is mainly used because of its reliability and its past achievement. A positioning-controlling apparatus using this incremental type linear encoder according to the prior art is described with reference to the accompanying drawings.
FIG. 8 schematically shows the arrangement of a positioning-controlling apparatus according to the prior art which uses the incremental type linear encoder (hereinafter, simply referred to as a linear encoder). The system shown in FIG. 8 may be considered as the essential portion of the X-direction driving unit used by the part-mounting equipment (100) shown in FIG. 7. As seen in FIG. 8, mounted on the servo motor (1) is a moving mechanism comprising a ball screw (3) for moving a subject (an object) (4), and a moving member (7) screwed on the ball screw (3). The subject (4) (the mounting head (75) in the case of the X-direction driving unit shown in FIG. 7) is secured on the moving member (7), and the subject (4) is moved in the direction R or L via the rotation of the ball screw (3) by the reciprocal rotation of the servo motor (1). The subject (4) is equipped with a linear encoder (5) which performs position detection by detecting a linear scale (6) secured parallel to the ball screw (3). A rotary encoder (2) which rotates together with the servo motor (1) to detect a rotation amount is coaxially mounted on the servo motor (1).
At the time of turning on a power supply, the servo motor (1) using the linear encoder (5) as a position-detecting means cannot grasp an absolute position of the subject (4). Therefore, the subject (4) needs to be returned to an origin position which is preset as a reference position, and then a relative position from the origin position is detected by counting output signals from the linear encoder (5) so as to make positioning control. A detection piece (8) is attached to the moving member (7) on which the subject (4) is mounted, so as to detect the returning of the subject (4) to the origin position. Further, an origin sensor (11) is arranged at the origin position, and the sensor (11) detects the detection piece (8) which has been moved to the origin position.
The servo driver (10) controls the rotation of the servo motor (1) according to an instruction from the controller (9) which controls the overall operation of the equipment, and also according to a detection signal from the origin sensor (11) and output signals from the rotary encoder (2) and the linear encoder (5). Inside the servo driver (10), generally, the velocity of the servo motor (1) is detected based on the position data from the rotary encoder (2) and the detected velocity is used for computation of the velocity of the servo loop, and the position data from the linear encoder (5) is used for computation of the position of the servo loop. However, in the case in which a moving mechanism for the subject (4), for example, a vibrating component such as the ball screw (3), is included, the position data and the velocity data from the linear encoder alone may be used for computation of the servo loop.
Next, the subject""s origin returning operation by the positioning-controlling apparatus shown in FIG. 8 is described with reference to the flowchart shown in FIG. 9. The origin returning operation starts when the controller (9) instructs the servo driver (10) to move the subject (4) in a predetermined direction at Step S1. The servo driver (10) simultaneously starts an origin sensor-retrieving operation for monitoring the input of a reference position signal (a signal to be inputted when the origin sensor detects the detection piece attached to the moving member (hereinafter referred to as the ON state of the origin sensor)) from the origin sensor (11) at Step S2. At this point in time, if the subject keeps moving because the Z phase is not detected by the linear encoder at Step S5 (No) after the origin sensor (11) has already entered the ON state (Yes) at Step S2, and if the origin sensor (11) then enters the OFF state (No) at Step S2, it is decided at Step S3 that the origin sensor (11) has once entered the ON state and then enters the OFF state. In this case, the moving direction is inverted at Step S4. If a condition for completing the origin returning operation is established at Step S5 (in other words, if the AND condition of the detection of the Z phase by the linear encoder and the ON state of the origin sensor is established), the servo driver (10) stops the moving operation at Step S6, and the controller (9) stops the instruction and completes the subject""s origin returning operation.
In the positioning-controlling apparatus with the above arrangement, the origin is defined as a position of the Z phase detected by the linear encoder (5), which is capable of accurately detecting the position of the subject (4). On the other hand, the Z phase detected by the rotary encoder (2) is used as a reference for generating an electrical current instruction with sine waveform pulses for driving the servo motor (1). That is, the position of the Z phase detected by the linear encoder (5) is used to determine the position of a spatial absolute reference origin, and the position of the Z phase detected by the rotary encoder (2) is used to determine an electrical origin (a reference for determining timing for an electrical waveform which composes an operational instruction to the servo motor, that is, a reference for synchronization of servo control) necessary for controlling the servo motor (1).
Next, a method of driving the servo motor (1) is described with reference to FIGS. 10 and 11. The servo motor (1) is driven according to rectangular waveform pulses as shown in the lower half of FIG. 10, based on a CS phase (commutation signal phase) which is outputted in accordance with positive or negative induced voltage of the motor. That is, when the position of the subject (4) is present at, for example, position A shown in FIG. 10, CS signals 1 and 3 are in the ON state, which leads to a control for allowing current to flow on U, W. When the servo motor (1) is present at position B in FIG. 10, CS signals 1 and 2 are in the ON state, and a control for allowing a current to flow on U, V is performed.
The above CS phase is a generic name of CS1 to CS3. Specifically, CS1 is a rectangular waveform pulse corresponding to positive or negative induced U-W. Similarly, CS2 is a rectangular waveform pulse corresponding to positive or negative induced voltage V-U, and CS3 is a rectangular waveform pulse corresponding to positive or negative induced voltage W-V. As shown in FIG. 11, in the servo motor, the notations U, V and W refer to motor power lines for three-phase driving. In detail, U-W indicates the induced voltage of the motor power line U obtained when the power line W is grounded (represented by G). Similarly, V-U indicates the induced voltage of the power line V obtained when the power line U is grounded, and W-V indicates the induced voltage of the power line W obtained when the power line V is grounded. The driving by rectangular waveform pulses is employed for constructing a motor at lower cost because the driving control is possible only by using a combination of the above three CS signals alone, which leads to simple driving, or it is employed for driving before the completion of the subject""s origin returning operation just after the power supply is turned on, as mentioned above. This driving mode, however, may not be employed for the essential use of the servo motor (1) for performing high-speed and high-accuracy driving, because of the limited performance by this driving mode.
To solve this problem, the performance of the servo motor (1) is drawn by sine waveform pulse driving. The sine waveform pulse driving is carried out as follows. The Z phase detected by the rotary encoder (2) is defined as a reference for an electrical origin of the servo motor (1), and an electrical distance from this electrical origin is computed based on the A phase and B phase from the rotary encoder (2). The result is outputted as a sine waveform pulse current instruction in proportion to the induced voltage from the servo motor (1) as shown in the upper half of FIG. 10. In FIG. 10, the position of the Z phase detected by the rotary encoder (2) is caused to coincide with the rise of the CS 1 signal, and it is possible to estimate an electrical axial position of the servo motor (1) from the position of the Z phase and the count values of the A phase and the B phase per one rotation of the rotary encoder (2). Thus, the sine waveform pulse driving of the servo motor (1) becomes possible. This sine waveform pulse driving is suitable for high-accuracy driving because an electrical angle can be found by an encoder resolution per one rotation, so that it becomes possible to increase the acceleration and to use the servo motor up to the uppermost limit of its performance. The sine waveform pulse driving is generally performed in part-mounting equipment, because the rectangular waveform pulse driving of the servo motor (1) makes it hard to reduce the positioning-settling time and to achieve constant velocity required for recognition of parts. However, the reference for sine waveform pulse can not be obtained before the Z phase is detected by the rotary encoder (2), as in the case immediately after the power supply is turned on. Therefore, the sine waveform pulse driving may not be realized during such a time frame. In such a case, the foregoing rectangular waveform pulse driving is performed until the Z phase is detected by the rotary encoder (2). Then, at a point of time when the rotary encoder (2) detects the Z phase, the sine waveform pulse driving becomes possible, and the driving is switched to the sine waveform pulse driving.
The conventional servo motor (1) is equipped with the rotary encoder (2) capable of detecting A phase and B phase for use in detecting a rotation angle, Z phase for indicating the position of the origin, and CS1 to CS3 phases corresponding to positive or negative of induced voltage of the motor. If the servo motor (1) is provided on the above positioning-controlling apparatus or the like, the linear encoder (5), in many cases, is used for controlling a position and velocity in the servo loop and detecting an absolute origin position. Therefore, it is rare to provide the linear encoder (5) for detecting an electrical origin and CS phases because of the difficulties in adjustment thereof.
The operation of part-mounting equipment provided with the above positioning-controlling apparatus is described with reference to the flowchart shown in FIG. 12 in conjunction with FIG. 7 already described above.
As mentioned above, the latest part-mounting equipment is required to meet the demand of high-speed and high-accuracy performance in association with miniaturization of parts. To solve this problem, advanced synchronous control employing multi-axial driving such as twin-axial driving is used, especially for the Y-direction driving unit of the robot (60). In this example, the synchronous control of the motor (62) and the motor (64) of the above Y-direction driving unit for the Y-directional operation of the beam (70) which supports the mounting head (75) is described. When the power supply is turned on, the current positions of the motors (62 and 64) are not known, and therefore, they are caused to return to the origin positions, respectively. This origin-resuming operation is carried out according to the method disclosed in Laid-Open Japanese Patent Publication No. 11-J45694/1999 or the like. The summary of the method is illustrated in the flowchart shown in FIG. 12. The flowchart of FIG. 12 illustrates a case in which the origin-resuming operation described in the flowchart of FIG. 9 is essentially performed on each of the plurality of axes. That is, at Steps S15 and S21 of the flowchart on FIG. 12, the origin positions of the mounting head (75) as the subject (4) are independently detected relative to the motors (62 and 64) so as to complete the mounting head""s returning to the origins on the respective ball screws (63 and 65), and thus, at Steps S16 and S22, the subject""s returning to the origins on the twin axes are completed. In this connection, the acceleration and the velocity of the motors at the time of the origin returning operation are controlled lower on the assumption that the rectangular waveform pulse driving should be done, and therefore, the performance of the motors may not be important at the time of the origin-returning operation.
However, the positioning control according to the prior art described above has the following problem. There is a possibility that the subject""s origin-returning may be completed before the rotary encoder detects the Z phase, depending upon a position at which the origin-returning operation is started or upon a subject""s moving direction. This is because the condition of completing the origin-returning operation is based on the AND condition of xe2x80x9cdetection of the Z phase by the linear encoderxe2x80x9d and xe2x80x9cthe ON state of the origin sensorxe2x80x9d. The situation of this origin-returning operation is described in detail with reference to FIG. 13. Assuming that the position of the subject (4) when the power supply is turned on is at P1 on FIG. 13, and the subject""s returning direction to the origin is negative (the left direction on the drawing). Under such an assumption, the subject (4) starts returning to the origin, and keeps moving when the rotary encoder (2) first detects the Z phase (indicated by the notation X) and then stops when the linear encoder (5) detects the Z phase. Thus, the subject""s origin returning is completed. In this case, the driving mode of the servo motor (1) is switched to the sine waveform pulse driving from the rectangular waveform pulse driving at a point of time when the rotary encoder (2) has detected the Z phase once, as shown in FIG. 13. Therefore, the servo motor (1) can be driven at high acceleration or deceleration and at high velocity so as to control the positioning after the completion of the subject""s origin returning, because this driving is done according to the sine waveform pulses obtained after the above switching. Thus, the driving of the apparatus which drives the subject (4) is performed without any problem.
In another case in which the position of the subject (4) when the power supply is turned on is at the position P2 on FIG. 13 and the direction of the subject""s returning to the origin is positive (the right direction on the drawing), the subject (4) keeps moving until the linear encoder (5) detects the Z phase, while the rotary encoder (2) does not detect the Z phase at all. Thus, the subject""s returning to the origin is completed at the time of the detection of the Z phase by the linear encoder (5). In other words, in spite of the completion of the subject""s returning to the origin, the servo motor (1) is still driven according to rectangular waveform pulses, because the rotary encoder (2) does not yet detect the Z phase. In this case, if the subject""s moving direction is negative as shown in FIG. 13 in the positioning operation after the completion of the subject""s returning to the origin, it is understood that the servo motor (1) is still driven according to rectangular waveform pulses for a period of time while the rotary encoder (2) rotates once at the most until the first Z phase is detected by the rotation of the rotary encoder (2). After that, just when the rotary encoder (2) detects the Z phase, the rotating servo motor (1) is abruptly driven according to sine waveform pulses which are switched from the rectangular waveform pulses.
In actual part-mounting equipment, the first origin returning operation just after the power supply is turned on is performed while acceleration and velocity are lower, assuming the driving in accordance with rectangular waveform pulses. Therefore, the equipment is operated without any problem, even if driven according to rectangular waveform pulses. However, the positioning-controlling operation after the completion of the subject""s origin returning is performed at high acceleration and high speed. Under such a condition, if the servo motor (1) is still driven according to rectangular waveform pulses, abnormal noises occur and constant velocity is lost. Thus, the servo motor (11) can not perform the essential positioning control. Further, if the driving mode of the servo motor (1) accelerating is switched from the rectangular waveform pulse driving to the sine waveform pulse driving, a rapid change in torque arises, which leads to occurrence of abnormal noises and pulsating speed.
As mentioned above, in order for the latest part-mounting equipment to meet the demand of high-speed and high-accuracy performance, the advanced synchronous control by multi-axial driving such as twin-axial driving is done on the robot. If the above linear encoder system positioning-control according to the prior art is applied to such synchronous control, a highly synchronizing operation becomes impossible during the acceleration step, depending on the condition of completing the origin returning operations on the multiple screws. As a result, the beam (70) (see FIG. 7) may be twisted in the X-axial direction, which adversely influences the accuracy and lifetime of the equipment. Particularly when the power supply of the part-mounting equipment is turned off, the subject is generally returned to the origin position or around the origin position in order to prevent interference among the axes. By doing so, in most cases, the mounting head as the subject is positioned at or around the origin of the linear scale when the power supply is turned on the next time. When the power supply is again turned on under this condition so as to carry out the first subject""s origin returning operation, such events frequently occur that the linear encoder detects the Z phase before the rotary encoder detects the Z phase, thereby completing the subject""s origin returning. This provides a serious problem in that adverse influences inevitably impact the accuracy and lifetime of the beam (70) along the direction X at every time when the power supply is turned on. Under these circumstances, an advanced positioning-controlling apparatus capable of solving the foregoing problems is desired.
The present invention is made in order to solve the above-mentioned problems by adding, to the condition of completing the subject""s origin returning operation, a condition that the rotary encoder should detect the Z phase prior to the Z phase detection by the linear encoder, in a positioning-controlling process. Specifically, the present invention provides the following.
One aspect according to the present invention relates to a positioning-controlling apparatus which comprises a servo motor, a servo driver for controlling the driving of the servo motor, a rotary encoder for detecting the rotation amount of the servo motor, a moving mechanism driven by the rotation of the servo motor, and a linear encoder for detecting the moving amount of the moving mechanism. The servo driver detects, from the rotary encoder, a CS phase necessary for driving the servo motor, and generates a current instruction with rectangular waveform pulses which are obtained from the CS phase from the rotary encoder until the time when the rotary encoder detects a Z phase or the linear encoder detects a Z phase. After the rotary encoder detects the Z phase or the linear encoder detects the Z phase, the servo driver generates a current instruction with sine waveform pulses based on the Z phase detected by the rotary encoder, thereby switching the driving mode of the servo motor. At the time of turning on a power supply, the servo driver returns a subject to be moved by the moving mechanism to an origin position which is the position of the Z phase detected by the linear encoder, and then, moves the subject to a required position and stops it there for positioning. The rotary encoder detects the Z phase previously in the operation of returning the subject to the origin. By adding the condition that the rotary encoder should previously detect the Z phase to the condition of completing the subject""s return to the origin position, the driving of the servo motor for positioning the subject can be previously switched to the driving according to sine waveform pulses.
The above subject is completely returned to the origin and stopped there under the condition that, while the subject is being moved by the moving mechanism to return to the origin position, an origin sensor first detects that the subject is within a detectable region of the origin sensor, and the rotary encoder detects the Z phase. Then, the linear encoder detects the Z phase, while the subject is moving within the above detectable region.
The subject is not completely returned to the origin and continues to move under the condition that, while the subject is being moved by the moving mechanism to return to the origin position, the origin sensor first detects that the subject is within the detectable region of the origin sensor, and the linear encoder xe2x80x9cdetectsxe2x80x9d (i.e., encounters) the Z phase before the rotary encoder detects the Z phase while the subject is moving within the above detectable region. Thus, the linear encoder ignores the Z phase, so that the Z phase is not detected by the linear encoder at this time. The subject is completely returned to the origin and stopped there under the condition that the subject is kept moving to leave the above detectable region and is then moved in the reverse direction to again enter the detectable region. Thus, the rotary encoder detects the Z phase and the linear encoder detects the Z phase in this order, while the subject is moving within the above detectable region.
In a positioning-controlling apparatus according to another aspect of the present invention, the subject is moved by the moving mechanism to return to the origin which is the position of the Z phase detected by the linear encoder, as follows. The subject""s moving direction for returning to the origin position is predetermined, and the origin sensor, the Z phase to be detected by the rotary encoder and the Z phase to be detected by the linear encoder are adjusted so that, while the subject is moving to the predetermined direction, the origin sensor can first detect that the subject is within the above detectable region, then that the rotary encoder detects the Z phase, and then that the linear encoder can detect the Z phase.
In the positioning-controlling apparatus according to the above aspect, if one end of the subject""s movable region coincides with one end of the above detectable region, the Z phase to be detected by the linear encoder and the Z phase to be detected by the rotary encoder are arranged so that first the rotary encoder detects the Z phase and then the linear encoder detects the Z phase while the subject is moved toward the one end of the above detectable region from the other end thereof.
Further, when the position of the above subject at the start of the subject""s origin returning operation is outside of the above detectable region, the subject may be moved in a predetermined direction specified as the moving direction for returning to the origin position, so as to be returned to the origin.
Further, when the position of the subject at the start of the subject""s origin returning operation is within the detectable region, the subject may be moved in a direction reverse to the predetermined direction specified as the moving direction for returning to the origin position, so as to leave the above detectable region, and then be moved in the reverse direction which is the above predetermined direction, so as to be returned to the origin position.
In a positioning-controlling apparatus according to yet another aspect of the present invention, an offset amount and an offset direction, which are the distance and the moving direction from the position where the rotary encoder detects the Z phase to the position where the linear encoder detects the Z phase, are predetermined. The above servo driver switches the driving mode according to the current instruction with rectangular waveform pulses to the driving mode according to the current instruction with sine waveform pulses, when the subject is moved in the offset direction by the offset amount from the position where the rotary encoder detects the Z phase. In this aspect, the current instruction with rectangular waveform pulses is not immediately switched to the current instruction with sine waveform pulses even when the rotary encoder detects the Z phase, and this switching is executed when the linear encoder detects the Z phase, or the subject is moved by the offset amount after the Z phase is detected by the rotary encoder.
Yet another aspect according to the present invention relates to part-mounting equipment which comprises a circuit-formed material-holding device for carrying and holding a circuit-formed material, a part-supplying unit for supplying parts, a mounting head capable of taking a part out of the part-supplying unit and mounting the part on the circuit-formed material, a robot for carrying the mounting head, and a controller for controlling the circuit-formed material-holding device, the part-supplying unit, the mounting head, and the robot. With this arrangement, the part taken out of the part-supplying unit by the mounting head is mounted on a mounting position of the circuit-formed material, wherein either or both of the robot and the circuit-formed material-holding device comprise(s) any of the above positioning-controlling apparatuses in order to accurately position the part at the predetermined mounting position of the circuit-formed material.
In this part-mounting equipment, the robot or the circuit-formed material-holding device may comprise a multi-axial driving unit for synchronous operation using a plurality of servo motors, so as to carry the mounting head or the circuit-formed material in a predetermined direction. That is, the positioning-controlling apparatus of the present invention may be applied to part-mounting equipment comprising a multiaxial driving system with high accuracy and high load durability.
A further aspect according to the present invention relates to a positioning-controlling method which comprises the steps of driving a servo motor, which is a driving source for moving a subject, according to a current instruction with rectangular waveform pulses obtained from a CS phase detected by the above rotary encoder until the time when the rotary encoder which detects the rotation amount of the servo motor detects a Z phase or the linear encoder detects a Z phase. The driving mode of the servo motor is switched to a driving mode according to a current instruction with sine waveform pulses based on the Z phase after the rotary encoder detects the Z phase or after the linear encoder detects the Z phase. The subject is returned to the origin position which is the position of the Z phase detected by the linear encoder which detects the moving amount of said subject, and then the subject is moved to a required position so as to position the subject. A condition that the rotary encoder should previously detect the Z phase is added to the condition of completing the subject""s origin returning operation. By the addition of this condition, the driving mode of the servo motor is previously switched to the driving mode according to sine waveform pulses for positioning the subject.
In the above positioning-controlling method, the subject""s moving direction for returning to the origin position may be predetermined, and the origin sensor, the Z phase to be detected by the rotary encoder, and the Z phase to be detected by the linear encoder may be adjusted so that the origin sensor can first detect that the subject is within the above detectable region. The rotary encoder detects the Z phase and the linear encoder detects the Z phase in this order, while the subject is being moved in the above detectable region. That is, the timing of the detection of the subject by the origin sensor, the detection of the Z phase by the rotary encoder, and the detection of the Z phase by the linear encoder is adjusted so that the driving mode of the servo motor for positioning the subject can be previously switched to the driving mode according to sine waveform pulses before the positioning operation.
A further aspect according to the present invention relates to a part-mounting method which comprises the steps of taking a part out of the part-supplying unit; carrying the part to a mounting position of a circuit-formed material which is regulated and held; positioning the part there; and mounting the part at the mounting position. The foregoing positioning-controlling method is employed for either or both of positioning a mounting head for holding and carrying the part and a holding device for regulating and holding the circuit-formed material, in order to accurately position the part to the predetermined mounting position of the circuit-formed material.